North Raccoon River IA 04-RAC-1132
from confluence with Indian Cr. (S24 T87N R36W Sac Co.) to confluence with Cedar Cr. in S25 T88N R36W Sac Co.
- Assessment Cycle
- 2018
- Release Status
- Final
- Data Collection Period
- Overall IR Category
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trend
- Unknown
- Created
- 5/29/2019 10:51:26 AM
- Updated
- 8/1/2019 1:53:35 PM
Assessment Summary
The Class A1 (primary contact recreation) uses are assessed as "not supported" due to levels of indicator bacteria (E. coli) that slightly violate state water quality standards. The Class B(WW1) aquatic life uses remain assessed as "partially supporting" based on results of DNR/SHL biological sampling in 2012, 2013 and 2015, 2016. The fish consumption uses remain not assessed. The sources of data for this assessment include (1) the results from the DNR/SHL ambient monthly monitoring station downstream from Sac City in Sac County (STORET station 10810001 (formerly station 423014)) located approximately 5 miles south of Sac City from 2014-2016, (2) results of USGS ambient monitoring near Sac City at station 05482300 from August 2012 through August 2013, and (3) results of DNR/SHL biological sampling conducted in 2012, 2013 and 2015, 2016.
Assessment Explanation
[Note 1: This assessment of the Class A1 (primary contact recreation) uses and the water quality data are used, in part, for the adjacent downstream segment (IA 04-RAC-1131).] [Note 2: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by DNR and approved by EPA in June 2008. Because this TMDL covers the primary Section 303(d) impairment identified for the 2006 assessment/listing cycle, this waterbody was moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 cycle. This waterbody remains in IR Category 4a for the current cycle.] The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2014 through 2016 at DNR station 10810001 near (downstream from) Sac City were as follows: the 2014 geometric mean was 292 orgs/100 ml, the 2015 geometric mean was 256 orgs/100 ml, and the 2016 geometric mean was 632 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Twelve of the combined 24 samples (50%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."
Results of chemical/physical water quality monitoring at DNR station 10810001 near (downstream from) Sac City, however, suggest “full support” of the aquatic life uses. Monitoring showedno violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.8 mg/L), 36 Dissolved Oxygen samples (minimum = 5.9 mg/L), 36 Temperature samples (maximum = 25.3° c), 36 Chloride samples (maximum = 93 mg/L), or 36 Sulfate samples (maximum = 220 mg/L) occurred during monitoring from January 2014 to December 2016.1 of the 35 samples (3%) analyzed for pH (range = 7.3 to 9.1) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as pH suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.
Assessment Key Dates
9/10/2012 | Biological Monitoring |
8/12/2013 | Biological Monitoring |
7/27/2015 | Biological Monitoring |
1/13/2014 | Fixed Monitoring Start Date |
12/8/2016 | Fixed Monitoring End Date |
8/11/2016 | Biological Monitoring |
Methods
230 | Fixed station physical/chemical (conventional plus toxic pollutants) |
315 | Regional reference site approach |
320 | Benthic macroinvertebrate surveys |
380 | Quantitative physical habitat assessment |
420 | Indicator bacteria monitoring |